As is well known, the aircraft industry is in a perpetual program to improve its products and in particular the engine manufacturers are constantly looking for a longer lasting combustor. This, of course, is occasioned by the need not only for improving the life and maintainability of the engine but also to improve fuel consumption by improving engine performance. Generally, one of the consequences resulting from increasing engine performance is the raising of the temperature at which the combustor is fired. This has given rise to investigating not only new materials but also different combustor liner constructions and cooling techniques.
This invention addresses a new scheme for fabricating the liners that form the combustion chamber. As will be appreciated, current burners in gas turbine engines are made of ductile alloys in a full hoop configuration. The primary cooling mechanism is the use of compressor discharge air for film cooling. The structure that allows the film to be injected into the combustion zone promotes the hot wall/cold wall thermal fight that ultimately leads to failure. The trend in advanced designs is to depart from the full hoop concept in favor of a series of discrete segments. The use of the segments allows higher temperature "turbine" alloys to be used to better withstand the operating environment. The intent is to reduce the thermal fight to increase life.
Unfortunately, the use of segments introduces a leakage path around each segment that must be sealed. In sealing this, some current designs reintroduce the thermal fight into the segment. This causes high stress in the segment and ultimately causes failure due to thermal fatigue.
We have found that we can obviate the problems alluded to above by prestressing the liner wall that confines the combustion products and forming the combustor by a plurality of segments that are segmented in the circumferential and axial directions. According to this invention each segment is formed from a flat blank into a curved-like member and is disposed to overlie a support frame that has four sides depending from a flat plate. The upper surface of each of the sides is contoured to a predetermined shape that conforms to the shape the prestressed wall will assume when at its intended temperature occasioned by firing the combustor. Clamping the segment to bear against the upper surfaces serves to seal the edges of each segment. It should now be obvious to one skilled in the art that each segment could as well be formed from a curved blank into a flat-like member.